The responses of fused taper couplers with different structure parameters to ultrasonic waves have been investigated theoretically and experimentally. A comprehensive analysis of the acousto-optic interaction was presented, taking into account the elasto-optic geometric effect. It is found that direct deformation of the coupler induced by ultrasonic waves is the critical factor in the sensing mechanism and is closely related to the sensor sensitivity. Moreover, the strain response of the coupler with different structure parameters was analyzed using a 3D coupled acoustic-solid numerical model, which was based on the developed mathematical model. According to the theoretical analyses, related experiments were carried out, and experimental results show that this ultrasonic sensor with a longer stretching length has higher sensitivity and the sensitivity of the sensor takes a nonmonotonic relation with an aspect ratio, which are consistent with the theoretical analyses results. We argue that our work may provide a useful guide in designing and optimizing more sensitive ultrasonic sensors used in practical ultrasonic detection.
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